The long-term objective of this K-award is to develop an effective weight management intervention for overweight and obese adults with multiple sclerosis (MS) and rheumatoid arthritis (RA). MS and RA make good disease models to adapt the proposed intervention because they manifest similar symptoms, but are distinct enough to allow for the possibility that the intervention could be generalized across different disabling conditions in future research. The premise of this proposal is that the consequences of energy imbalance create a pro- inflammatory state that may accelerate disease progression and disability. To reduce the impact of this inflammatory state, behaviors associated with energy balance need to be addressed (ie, sleep, nutrition, and physical activity). However, these behaviors are hard to change, particularly among people with disabling conditions who often experience symptoms as barriers to a healthy lifestyle. Thus, a novel approach is needed to promote behavior change. SystemCHANGE (SC) is a promising new behavior change program that uses approaches consistent with social ecological theories and focuses on re-designing the social environment using a multiple series of small, trial-and-error experiments. Thus, the goal of this K-award application is to obtain a skill set to develop a program of research on adapting and testing SC weight management interventions for adults with MS and RA. The existing SC intervention targets improvements in eating, physical activity, and sleep. To make the intervention relevant to people with MS and RA, we will adapt the intervention to also support self-management skills related to pain, fatigue, depression, and stress/anxiety. The training aims of this proposal are to obtain an understanding of how to adapt and test the SC intervention using objective measures of upper and lower extremity function as well as to increase analytical and general research skills. The research aims of this proposal are to engage potential participants and their families as co- designers to adapt the SC intervention, conduct a formative evaluation of the intervention, and then conduct a randomized controlled pilot study (n=60) to provide preliminary estimates of the SC intervention's efficacy. The pilot study will provide estimates of effect size on the following primary outcomes: phenotypic indices of energy balance (e.g., weight, body fat percent), self- report measures of symptoms (e.g., fatigue and pain) and social participation, and objective measures of upper and lower-extremity function. The proposed pilot is significant because of its potential to address three of the most perplexing and prevalent health problems that we face today--inflammatory autoimmune diseases, disability, and obesity with a novel intervention.